Pressure cooker



' Jan. 19, 1943.

M. H. GRAHAM PRESSURE cooxER Filed Feb. '7, 1941 2 Sheets-She't 1 A ttor n e y Jan. 19, 1943. M. H. GRAHAM l PRESSURE cooKER R 2 MH/ O t 4 m E h V s N my .l L e .e h S 2 z. M v, b. U e F d lo m 4 .l

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am www 'Attorney Paieeied Jamie, 1943 UNITED ASTATES PATENT OFFICE l 2,308,603 rarissima cooxna Maurice H. Graham, St. Louis Park. Minn. Application February 7, 1941, serial No. 377,896

'(ci. 21e- 43) 18 Claims.

The present device relates to new and useful improvements in pressure cookers and has for a 4broad object the automatic regulation of heat flow from a source o! heat to a pressure cooker.

A further object of the invention is to provide an autmatic cut-out for the heating means of a pressure cooker which is operated in re- -sponse to the pressure within the pressure cooker.

Another object ci the invention is to provide means for automatically releasing the air from within the pressure cooker so that it will attain "the proper temperature at a given pressure.

A still further object is to provide a pressure cooker which will operate economically, conserving heat through a minimum of steam escapage.

In the ordinary pressure cooker as is weil known .in theart, it is necessary for the user to watch the pressure gauge lof the cooker so as to adjust the heating means and the rate of heat now to the cal escape of steam. In the present device the pressure control maintains the proper cooking conditions within the cooker without wastingheat in the form of escaping steam.

Further, the presence of air in pressure cooking devices at the beginning oi! the heating operation has heretofore caused much trouble in attaining proper cooking conditions. The pressure cooker operates on the principle that an increase in pressure increases the boiling point oi water 1and thereby raises the cooking temperature correspondingly. For example, saturated steam at a pressure of fifteen pounds per square inch has a temperature of about 249 Fahrenheit. It is to` be observed, however, that the temperature and pressure stated correspond only in the case where the vapor phase comprises pure steam. Where air plus steam comprises the vapor phase the temperature will be much less, being approximately what the temperature or pure steam would be at the pressure equal to the fraction or the total pressure contributed by the steam alone in the air plus steam phase. Thus where a pressure of iifteen pounds per square inch above atmospheric pressure is maintained and the steam constitutes l half the pressure and air the other half, the eiective steam pressure is only 7.5 pounds per square inch. The corresponding temperature i'or 234 Fahrenheit. vWhere the user of a pressure cooker is aware of this phenomenon it has been the practice for him to manually release the air from the cooker while pressure is'building up or to overheat the cooker in order to cause the pop-of! valve to release the air from the cooker. When the air is thus released from the cooker in the above example, the temperature will increase from 234 to 249 F., which latter temperature is the correct operating temperature for the cooker. In the present device the air release is an automatic function which accompanies every cooking operation and requires no special atten-l g tion.

' The present invention contemplates a pressure controlled source of heat operating at a predetermined pressure and a pop-oir valve operating at another pressure slightly greater than that of the pressure control. During the initial heating operation there is a lag in the transfer of heat to the cooker and from the cooker to its contents due to the heat capacity of the device as a whole.

For this reason the heat transfer to the cooker and its contents continues and the pressure increases even after the heater has been deenergized by the pressure control. The pop-oi! pressure in this initial heating operation is exceeded because of heat lag in the transmission o! heat from the heater to the cooker, and the air is automatically expelled from the cooker. Now, however, since the device has reached an equilibrium between heat input and heat losses, the pressure control subsequently operates more nearly in accordance with fluctuations in temperature and the pop-oir pressure is not again reached during that cooking operation. The single popof! action, however, sulilces to expel the air from the-cooker.

In the drawings:

Figure 1 is a side elevation ci the'pressure cooker;

Figure 2 is a detailed view in vertical section on the lines 2--2 or Figure 4 showing the weight valve and the spring valve with the pressure cooker in operative position; v Figure 3 is an .enlarged sectional view of the spring valveand the socket connection with the pressure cooker withdrawn from operative position:

Figure 4 is an elevation oi' the pressure cooker as viewed in the direction or thearrows I--l ci 1- v Figure 5 is' a detailed 'side view of the pressure control mechanism as shown in Figure 1 with part l actuated steam at 7.5 pounds pressure is about 5s cut away to show the construction; and

Figure 6 is a horizontal section taken on the lines 8 8 of Figure 5. i

Referring more particularly to the drawings, Figure 1 shows a pressure cooker comprising a container 2 with a cover 4. The container 2 is equipped with a handle 8 and the cover 4 is equipped with a handle 8. The cover 4 is secured to the container 2 by any means which will give a pressure-tight connection, preferably by means adapted to seal the cover upon slight rotational movement of the handle 8 with respect to the handle 8 so as to bring the handles 6 and 8 into alignment when the cover is sealed. At the center of the cover 4 is a steam pressure gauge I0 for indicating the pressure Within the cooker and to eid in making adjustments on the pressure control device. A pop-oli' valve i2 is placed in the cover 4 to insure against accidental build-up of pressure. The pop-off valve may be of any type, for example a rubber cap device as shown in Figure l, or a spring-controlled valve.

Also secured to the cover 4 and communicating with the inside of the pressure cooker is a second pop-off valve which preferably comprises a tubular stem member i4 which is secured at its base to an opening in the cover 4,A and a weight member i 8 disposed at the upper end of the stem member. The weight member I8 is cylindrically shaped and hasa longitudinal bore i8, of a diameter larger than that of the tubular stem 4 so that the weight member may be placed over the stem as shown in Figure 2. At the end of the bore I8 and centrally disposed therein is a beveled projection which fits partially into the end of the passageway 22 of the stem i4 and rests on a correspondingly beveled seat in the end of the stem I4 to form a tight connection therewith. An annular flanged portion 24 at the bottom of the weight member i8 fits loosely about the stem |4 and aids in maintaining the weight member i8 seated squarely on the end of the stem.

A tubular connecting member 28 communicates with the passageway 22 and extends out horizontally from stem i4. IThe tube 28 has a central opening 28 at its outer end of smaller dimension than the inside diameter of the tube. A valve member 30 with a beveled head 32 ts in the opening 28 and the head 32 is adapted to flt tightly against a correspondingly beveled seat 34 at the inside of the opening 28. A spring 38 is positioned against an annular bushing 38 at one end of the tube 28 and the head 32 at the other end and normally urges the valve to closed position to prevent the escape of steam from the pressure cooker. The valve 30, however, has longitudinal grooves 40, shown more particularly in Figure 3, which allows steam to pass through the opening 28 when the head 32 is not positioned against its seat 34 as shown in Figure 2.

The container 2 rests on a heater 42 which may be provided with suitable handles 44 and legs 48. The electric heating elements within the heater 42 are supplied with current from the terminals 41 and 48 and upon the closing of the pressure responsive switch to be described hereinafter.

A bifurcated bracket member 50 has its two legs secured to the heater 42 by means of screws 52 which extend directly through the base of the heater and screws 54 which extend into the horizontal supporting members 58.

The bracket member 50 has a central upward extension 58 which carries a short tube 80 into which is threaded a flared socket 82 which is adapted to receive the above described tubular connecting member 28.

The socket 82 has a central passageway 84 communicating with the interior of the tube and thence with the pressure responsive device to be described hereinafter. The passageway 84 is counterbored at 88 for a short distance to receive the projecting end of the valve member 88. When the tubular connecting member 28 is in operative position, the shoulder 88 of the counterbore holds valve 30 in open position. Preferably an annular gasket 10 is positioned within the socket 62 so as to prevent leakage of steam passing from tube 28 into tube 80 and the pressure responsive device now to be described.

A communicating tube 12 depends from the tube 28 and at its lower end it is connected to a pressure responsive bellows 14 which is surrounded by a housing 18. A base plate 18 is sccured in the bottom of the housing 18 by means of a U-shaped metal strap 80 through which passes the tube 12 and to which the housing is clamped by means of the nut 82. The base plate i8 is also secured to the bracket member 50 by means of screws 84, one of which appears in Figure 5.

The base plate 18 is provided at one edge with two upstanding ears adapted to pivotally engage the depending ears of a cross-piece 88. An arm 90 extending laterally from the cross-piece is thus free to swing through a short arc about a horizontal axis.

The upper surface of the arm 90 is engaged by a thrust rod 92 projecting downwardly from the lower end of the bellows 14. The under side of the arm 90 is preferably provided with an abutment 94 against which a spring-pressed thrust rod 08 exerts an upward pressure. The rod 98 is provided with a flange 58 and a spring |00 is compressed between the flange 98 and the upper end of a set screw |02. The set screw |02 is threaded in a shank |04 extending downwardly from the base plate 18 and makes possible an adjustment of the compression exerted by the spring |00. Since the bias of the spring |00 opposes the expansion of the bellows 14, the adjustment of the set screw |02 thus determines the amount of pressure necessary to move the pivoted arm 90.

'I'he switch for energizing and deenergizing the heater 42, includes a fixed contact |08 secured to the under side of a horizontal conducting arm |08 which is fastened to the post ||8 and connects with the wire ||2. The switch also includes a movable contact I|4 which is secured to the end of a spring conductor ||8 located beneath the movable arm 90 and connected to the wire H8. The spring conductor ||8 is enlarged intermediate its ends and has an opening |I8 through which members 98, 88 and 00 may move vertically, without establishing electrical contact therewith, as shown in Figure 6. The wires ||2 and ||8 are interposed between the heating element and the terminal 41. The other end of the heating element is connected to the terminal 48.

A non-conducting button |22 is fastened to the upper surface of the spring conductor ||8 and is positioned to be engaged by the downwardly curved end |24 of the arm 90 whenever the bellows 14 expands and lowers the arm 88 sufficiently. Owing to the upward bias of the spring arm l|8, the contacts |08 and ||4 are closed except when the arm 80 is moved downwardly as just described.

As shown, the terminals 41 and 48 may de- `:2,8Q8,008 'sirably be surrounded-'bye cylindrical housing -sequent pulling of the food by generation of ,llt

The heater s: is preferably proyidd with up- :standing'guide members l2. which insures that the receptacle 2 will be accurately positioned on f, 'the heater Awhen the device is in use.

In the operation of the device the user places .the: iood to .be cooked within the container l, v, -which may. now be separate from the heater member, and places the desired amount of water 4with the lood. .The cover .4 is then placed on .the container! and thehandle I and the cover are given a slight rotational movement so as to bring the handles and tinto augment and at the same timeseal the cover. 2 and its cover are then placed on the electric tube 2Q into the socket d2. .-'Ihecontainer 2 fits snugly between the upstanding guide members |28 and the tube 2t is thus held in pressuretight relation with the socket 82. The valve 3l enters the passageway o! the socket but engages the shoulder BI unseating the yvalve head 32 against the action of spring 38; A communieating passageway is thus established between the interior of the cooker and the bellows 14 through the grooves 40 in the valve 3l.

'I'he terminals 41 and Il are connected to a suitable source of electric power and the heater is energized through contacts I and IN which are now in closed relation as in Figure 5. :As

builds up within and is transmitted to the bellows 14 which begins to expand. At a predetermined cut-oiipressure, for example, fifteen The containerl -heater` 42 at thesame time introducing the the contents of the cooker are heated. pressure steam within the cell structure thereof. Likewise the pressure cooker may be used without the pressure control by merely setting the cooker on the heaterv so'that the tube 26 does not enter the socket I2, or the cooker may even be used' separately with any other source o! heat.

It is to be understood that the invention isV not limited to the particular embodiment herein ,adapted to remain closed during initial heating or the container to a predetermined pressure and becoming momentarily operative at said predetermined pressure to vent air trappedy in the container, and means responsive to the pressure within the container for regulating the, heater operative after said venting of air from the container to maintain the pressure within the container below the predetermined pressure at which the vent valve becomes operative.

'y 2. In a pressure cooking device, a closed container, a heater for the container, a vent valve responsive to pressure within the container adapted to remain closed during initial heating .oi the container to a nrst predetermined pressure and becoming momentarilyl operative at said first predetermined pressure to vent air trapped in the container, and means responsive to the pressure within the container for regulating the heater operative after said venting of air from-'the container to maintain the pressure within the container below said nrst predetermined pressure at which the vent valve becomes operative, said heater control means being operative when the container pressue exceeds a second predeterweight and the cross-section of the passageway n 22 of such area that a pressure of about-three pounds per square inch in excess of the prede. termined bellows cut-oi! pressure will raise the pop-oi! valve Il and allow vapor to escape-into the atmosphere until the pressure of the cooker falls back lbelow eighteen u pounds per square inch. The air present with the steam vapor escapes from the cooker when the pop-oi! valve u is raised by the initial evemde er heat. since the bellows breaks the contacts III, lll the override of heat is, therefore, not sumcient to raise the pressure to eighteen pounds per square inch and the pop-oi! valve will remain closed during the remainder of the operation.

The pressure cooker may be removed from the heater at any time whether or not there'is pressure within the cooker. It there is pressure within the cooker the valve Il will seal the opening in the tube 2l to prevent sudden-remined pressure, lower than said first predetermined pressure, to decrease the amount of heat applied to the container, and being operative when the container pressure falls below said second predetermined pressure to increase the amount of heat applied to the container.

3. In a pressure cooking device a closed con- -tainer, a heater for the container, means responsive to the pressure within the container for increasing the output of the heater when the pressure in the container is less than a first predetermined pressure and for decreasing the output of the heater when the pressure exceeds the nrst predetermined pressure and a valve operable to allow the escape of air andv steam from the contalner at a second predetermined pressure which is higher than the nrst predetermined pressure and attainable as the result of the initial heatlng action of the heater upon the container.l

4. In a pressure cooking device a closed container, a heater for the container, pressure-responsive means tor controlling the heater to norm-ally maintain a first predetermined pressure in the container and a relief valve operable to release air and steam at a pressure higher than mally maintain a nrst predetermined pressure in lease of the'pressure from the cooker and con- 1 5 the container and a relief valve operable to release air and steam at a pressure approximately three pounds higher than the first predetermined pressure.

6. In a pressure cooking device a closed container, an electric heater for the container, pressure-responsive means including a bellows-operated circuit breaker to normally maintain a first predetermined pressure in the container and a weighted pop-off valve operable to release air and steam at a second predetermined pressure higher than the first predetermined pressure and attainable as the result of the initial heating action upon the container.

7. In a pressure cooking device of the class including a closed container, a heater, a support for the heater removably mounting the container, and pressure-responsive means on the support for controlling the heater; Athe improvement which comprises fluid pressure conducting means rendered operative through the mounting of the container in operative positionupon the said support 'to provide a detachable iiuid pressure connection between the interior of the container and the pressure-responsive means.

8. En a pressure cooking device of the class including a closed container, a heater, a support ior the heater removably mounting the container, and pressure-responsive means on the support for controlling the heater; the improvement which comprises iiuid pressure conducting means leading from the container, adapted to be detachably connected with the pressure-responsive control means through the mounting of the container in operative position upon the support, and adapted to be detached from the pressure-responsive control means through the removal of the container from the support, and means rendered operative to seal said uid pressure conducting means against the escape of iluid pressure from the container when said conducting means is detached from the pressure-responsive control means upon removal of the container from the support.

9. In a pressure cooking device of the class including a closed container, a heater for the container, a support for the container and for the heater from which the container is removable, pressure-responsive means mounted on said support for controlling the heater; the improvement which comprises a tubular passageway leading from said container and another tubular passageway leading from said pressure control device, the ends of said tubular passageways being detachably joined together through bringing the container into operative position on said support and means provided on the said support whereby the said container is detachably fastened on the `said support in such a manner as to hold the said tubular passageways detachably secured in joined relationship.

10. In a pressure cooking device of the type comprising a closed container, a heater for the container, a support for the container and for the heater from which the container is removable, pressure-responsive means mounted on said support for controlling the heater; the improvement which comprises a tubular passageway leading from said container and another tubular passageway leading from said pressure control device, the end of one of said passageways being ilared outwardly to form a socket in which the end of the other passageway is detachably received through bringing the container into operative position on said support and means provided 0n the said support whereby the said container is 75 fastened in such a manner as to hold the said end of the other passageway securely in the said socket.

l1. In a pressure cooking device o! the type comprising a closed container, a heater for the container, a support for the container and for the heater, pressure-responsive means mounted on said support for controlling the heater; the improvement which comprises a rigid tubular passageway leading from said container and another rigid tubular passageway leading from said pressure control device, the end of one of said passageways being nared outwardly to form a socket adapted to lreceive the end of the other passageway when the container is in operative position on said support, and guide members on said support for maintaining the connection between the passageways.

l2. In a pressure cooking device oi the type comprising a closed container, a heater for the container, a support for the container and for the heater, pressure-responsive means mounted on said support for controlling the heater; the improvement comprising a iirst tubular passageway leading from said container, and another tubular passageway leading from said pressure control device, means for preventing the escape of vapor through the first passageway when the ends of said passageways are not connected t0- gether and means for connecting the ends of said passageways together when the container is in operative position on said support and for permitting the now of vapor from the iirst passageway into the second passageway.

13. In a pressure cooking device of the class including a closed container, a heater for the container, means responsive to the pressure within the container for decreasing the output of the heater when the pressure exceeds a predetermined pressure; characterized by, the fact that there is combined with the said means a valve arranged in such a manner as to allow the escape of `air and steam from the container at a pressure above the'predetermined pressure aforesaid and within the increase pressure range obtainable as the result of the override of heat from the initial action of the said heater upon the said container.

14. In a pressure cooking device of the class including a closed container, a support for the container and for the heater, pressure responsive means mounted on the said support for controlling the heater; the improvement which comprises a rigid tubular member projecting vertically from the said support, the said tubular member connected at the lower end to the said pressure responsive means, and the upper end of the said tubular member extending laterally, a second rigid tubular member projecting laterally from the said container, the said second tubular member having one end connected to the said container, an outwardly ared socket connected at one of the ends of the said tubular members, an annular resilient member positioned within the said socket and adapted to rit against an end of the other tubular member in such a manner as to permit the flow of vapor from the said container through the said tubular members to the pressure responsive means aforesaid, and means adapted to position the said container upon the said support in such a manner as to detachably secure the end of the other said tubular member within the said socket tightly against the said resilient member.

l5. In a pressure cooking device of the class I including a closed container, a heater for the Y control device, a valve member slidably mounted within one of the said tubular passageways, the said valve member adapted to operably close the said tubular passageway, and the said valve member having formed therein longitudinal grooves adapted to permit a flow of steam through the said tubular passageway when the said tubular passageway is connected with the other tubular passageway in such a manner as to slidably actuate the said valve so as to open the said tubular passageway.

16. In a pressure oookingdevice of the class including a closed container comprising a main section and a cover section removablyr secured to the main section, a heater for the main section and pressure-responsive means for controlling the heater; the improvement which comprises fiuidfpressure conducting means carried by the removable container cover section adapted to be rendered operative through operatively mounting the cover` section on the main container section to provide a detachable fluid pressure connection between the interior oi the container and the pressure-responsive control means.

17. In a pressure cooking device of the class including a closed container comprising a main' section and a cover section removably secured to the main section, a heater for the main container section and pressure-responsive control means for the heater; the improvement which comprises fluid conducting means carried by the removable cover section for transmitting fluid pressure from the interior of the container to the pressure-responsive control means, and detachable iluid coupling means adapted to automatically connect `said fluid pressure conducting means to the pressure-responsive control means through bringing the removable cover section into operative position on the main container section and to automatically break the connection between said uid pressure conducting means and said pressure-responsive control means through removal o! the cover section from the main container section.

18. In a pressure cooking device of the class including a supporting base, a closed container mounted on the supporting base, a heater for the container and pressure-responsive means for controlling the heater, both mounted on the supporting base, the container including a removable cover section independent oi the supporting base; the improvement which comprises a tubular passageway leading from the interior of the container and carried by the removable cover section, and another tubular passageway leading from the pressure-responsive control means, said tubular passageways having coacting end portions adapted to` be detachably joined through applying the coversection to the container on the supporting base.

MAURICE H. GRAHAM.l 

